The present invention relates generally to storage systems and, more particularly, to server image migration.
Rapid penetration of virtual server deployment in enterprise datacenters is one of the biggest trends in the IT world today. Not only the OS (operating system) itself but also Virtual Appliance (which is the coupled program image that is able to deploy on the hypervisor that is composed of OS, middleware and some objective dedicated application) is becoming a major option of virtual server image provisioning. It is a very easy thing to do since there are virtual appliances marketplaces (e.g., http://www.vmware.com/appliances) and the administrator can just download the program and will be ready to start it just as an appliance. Also, virtual server technology is one of the very important enablers for the cloud computing services. A wide variety of cloud services are emerging; it is believed that many enterprises will rely on the cloud services as one of the options for their IT resources.
As more virtual server deployment becomes easier, more virtual server sprawl has been seen recently. In addition, the size of each virtual server image (which means including required middleware and applications) has been rapidly growing due to the enrich functions. As a result of this combination, a datacenter needs to have a storage system of a very large size to hold virtual server images.
To optimize the total size of the virtual server images deployed in a datacenter, writeable snapshot technology has the potential to address the issue. For the use of writeable snapshot technology to reduce the virtual server image capacity, see, e.g., http://www.3par.com/SiteObjects/A7B11BEED3AC16DF15CA5A82011BF265/3PAR-sp-ds-08.1.pdf. Moreover, Fitzgerald disclosed a management technique of virtual server instances in US20080134175 A1. It mentioned having a snapshot-like configuration in the system. Also, it describes the virtual server image distribution behavior from the repository to a host. However, Fitzgerald did not teach how to reduce the data copy amount of the image during the migration, as disclosed in the present invention.
Because the deployment of a plurality of virtual server images has very large portion of redundant data due to the fact that they hold the same OS, middleware, and applications, and just a little portion of customized area, a snapshot mechanism works well to eliminate the redundant portion while keeping the presenting of the plurality of virtual server images (virtually). The original image is called the “Gold Image.” When a new virtual server instance is needed, a snapshot volume of the Gold Image will be created and connected to the virtual server. The snapshot volume is just a logical volume but the data read access can be done by actual read of the corresponding portion of data on the Gold Image. When a write access comes, it will then allocate a little capacity chunk to the snapshot volume and hold the specific data written, and this is the “customized part” from the original data of the Gold Image. With this virtualization technique only the customized data will be newly allocated and the original data part will not be allocated to the respective virtual server image volume. Thus, the total size of storage will be optimized.
However, a new issue is raised from a different aspect, namely, the size of data copy during virtual server migration between systems/sites. The deployment of virtual server technology has made it significantly easier to move server instance from one place to another, such as “VMotion” function of VMware. Typically the function is used to move virtual server instances from the test environment to the production site. However, from now on, the more dynamic use case such as for workload balancing within the total datacenter or disaster recovery use between local and remote sites will become more popular. Another major use case assumed involves moving virtual server from the enterprise on-premise datacenter to the outside cloud service system. Thus, there will be a huge potential for the case where the user needs to migrate a virtual server between datacenters. Unfortunately, although the writeable snapshot technology optimizes the capacity within a storage system by eliminating the redundant portion, when it needs to be transferred to somewhere outside of the system, such as a cloud service system, the whole size of the virtual server image needs to be transferred. Since each size of the image will become larger and the number of migration will become huge, a very large data size of (remote) copy will be needed.
A number of references disclose how to reduce the data copy amount when the replication source and destination volumes are fixed and originally configured in the first place. None of them teach minimizing the data copy size in the situation where the destination of the migration can be varied and be determined dynamically. See, e.g., U.S. Pat. No. 7,287,132 B2, U.S. Pat. No. 7,383,405 B2, U.S. Pat. No. 7,509,467 B2, US20060031637 A1, US20080244205 A1, and US20080320051 A1.